The present invention relates to an image pickup apparatus which is capable of generating an image signal to reproduce an image with high quality and high resolution.
Generally, improvement of the resolution of a reproduction image corresponding to an object taken by an image pickup apparatus such as a video camera depends upon an image signal produced through an image sensing device provided in the image pickup apparatus so as to sense an optical image from the object. In an image pickup apparatus of the type using an image pickup tube, or camera tube, as the image sensing device, because of the limitations imposed on microscopic reduction of the diameter of an electron beam in the image pickup tube, difficulty is encountered to attain the high resolution through the microscopic reduction of the electron beam diameter, and further since the capacity of a photo-electric conversion target of the image pickup tube increases in accordance with the area of the target, difficulty is also encountered to realize the high resolution by enlarging the target area. That is, due to the performance of the electron gun and the structure of the focusing system of the image pickup tube, there is a limit in increasingly heightening the resolution by the microscopic reduction of the diameter of the electron beam. Further, because of reduction of the high-frequency signal component of the output signal of the image pickup tube due to increase in a capacitance of the target capacity caused by increase in the target area, the S/N of the image pickup tube output signal is extremely deteriorated so as to make it difficult to adequately produce an image signal which can produce an image with high quality and high resolution.
In addition, in order to develop a reproduced image with high quality and high resolution in an image pickup apparatus equipped with a solid-state image sensing device, the solid-state image sensing device should be arranged to have a large number of pixels. However, such a solid-state image sensing device requires a clock signal with a high frequency in driving, and since the capacitance value of a driven circuit is heightened due to increase in the number of the pixels, such a solid-state image sensing device may be difficult to be arranged for a practical application when taking into account the fact that the limit of the frequency of the clock signal is 20 MHz.